Tridentate ligands diphosphines

Baratta and coworkers reported highly active and enantioselective ruthenium and osmium hydrogen transfer catalysts based on a combination of an amino P3rridine and a diphosphine ligands (263,264,266,267,324,325). The amino pyridines employed are l-substituted-l-(pyridine-2-yl)methanamines (I) or or-thometallated CNN tridentate ligands derived from II and III (Fig. 74). The diphosphine were PPh2(CH2)4PPh2, (S,iS)-Chiraphos, (SyS)-Skewphos, (S)-MeO-Biphep, (i2,i )-Diop, (S,K)-Josiphos (i ,S)-Josiphos, or (i ,S)- Bu-Josiphos. The source of chirality is the amino pyridine, the diphosphine, or both. Acetophenone and aryl-substituted acetophenones are reduced with TOF up to 1.4 x 10 h at 50% conversion and up to 99% ee. 

Reaction of diphosphines with the complex of a 6",iV,iV-tridentate ligand leads to the /i 6 -coordinated arylplatinum complex 634 or the dinuclear complex with the diphosphine ligand that bridges two Pt centers coordinated by bidentate arylimine ligands (635, Scheme 88). ... 

On the other hand, the enantioselective 1,4-addition of carbanions such as enolates to linear enones is an interesting challenge, since relatively few efficient methods exist for these transformations. The Michael reaction of p-dicarbonyl compounds with a,p-unsaturated ketones can be catalysed by a number of transition-metal compounds. The asymmetric version of this reaction has been performed using chiral diol, diamine, and diphosphine ligands. In the past few years, bidentate and polydentate thioethers have begun to be considered as chiral ligands for this reaction. As an example, Christoffers et al. have developed the synthesis of several S/O-bidentate and S/O/S-tridentate thioether... 

Pd(diphosphine)2](BF )2 and [Pd(PP2)(PR3)](BF )2 were prepared and evaluated. The presence of a monodentate phosphine ligand in the [Pd(PP2)(PRo)](BF >2 complexes permits a phosphine ligand to dissociate during the catalytic cycle. At the same time, the use of a tridentate phosphine ligand allows electrochemical reversibility to be preserved. 

Moreover, deconstructing the tridentate architecture of the triphos ligand into chiral diphosphines such as xyl-BINAP or SEGPHOS provided an enantios-elective cycloisomerization with enantio-ratios up to 98 2 (Scheme 31) (68). 

The tetracoordinated diphosphine complex [Rh(CO)2(dppoo)]C104 (P-P-O-coordinated, dppoo = (Ph2PGH2GH2 0GH2>2) was obtained.Calix[4]arene ligands with phosphorus-containing groups provided new tetracoordinated P-P-O-tridentate Rh-CO complexes, like 42. ... 

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